The present invention relates generally to a method for testing the stickiness of cotton using multiple temperatures.
In a spinning mill, cotton contaminated with excessive amounts of sugars causes serious problems, for it contaminates all the mechanical instruments used in the transformation process from fiber to yarn; i.e., opening, carding, drawing, roving and spinning operations. These contaminants are due mainly to sugar deposits produced either by the cotton plant itself (physiological sugars) or by feeding insects (entomological sugars).
The physiological sugars that are deposited on cotton have been analyzed using the aphis-stylet technique to obtain pure phloem sap from cotton plants to show that the major sugar translocated is sucrose ( greater than 90%). The presence of sucrose in the cotton lint reveals that the plant was still growing when the harvest occurred. Some sucrose was still translocated to the bolls in order to continue the growth process and to accumulate cellulose within the under-developed fibers. Mature bolls have low physiological sugar content, while immature bolls, still in the development phase, have high physiological sugar content. Also, harvest-aid chemicals cause some of these bolls to open. For this type of cotton plant the distribution of the sugars will not be even. The least developed fibers coming from such immature bolls tend to remain together in the form of entangled fibers and when ginned, the water content of this specific type of fibers at the breaking point is such that the physiological sugars are able to migrate from the inside of the fibers to the outside through the open lumen. This succession of events leads to a localized concentration of sugars similar to the one observed with honeydew.
Although the presence of physiological sugars is a problem when processing cotton, cotton stickiness is more often attributed to entomological sugars from insect honeydew than physiological sugars. The main honeydew-producing insects that infest cotton plants are the cotton white fly Bemisia tabaci (Gennadius) and the cotton aphid Aphis gossypii (Glover). White flies and aphids are both plant sap-sucking insects that feed by inserting their slender mouth-parts and the stylets into the leaf tissues. The sap is digested and ejected as a droplet of honeydew. The honeydew attaches itself to the leaves and the fibers of opened bolls. The ginning process scatters the honeydew, making it more difficult to detect with the naked eyes. Tests relating to these entomological sugars have been performed analyzing honeydew from Aphis gossypii and Bemisia tabaci. The testing found around 40% of melezitose in the aphid honeydew and 40% of trehalulose plus 17% of melezitose in the white fly honeydew. These percentages are different on contaminated lint water extract because of the physiological sugars.
Stickiness is a worldwide contamination problem as shown by the International Textile Manufacturers Federation (ITMF) Cotton Contamination Survey (Strolz, 2000). Every other year the ITMF organizes a survey by sending to spinners worldwide a questionnaire about the perception they have on the different cotton contaminations for the main origins of cotton. xe2x80x9cIn 1999, of the most important growths, Sudanese cottons remains the most affected with nearly 75% of all those having used these origins experiencing stickiness, followed by the average of all growths of West Africa (33.5%), Central Asia (25.3%), India (21.9%), and the US (18.6%). At the lower end of the scale follow Turkey (9%), Australia (9%) and Argentina (5%).xe2x80x9d Because of this worldwide contamination problem a variety of testing procedures to determine the stickiness of cotton have been developed.
One of the testing procedures is the Potassium Ferricyanide Reducing Sugars Test (Perkins test), which is based on the hypothesis that stickiness is caused by reducing sugars, mainly glucose, fructose and oxidized trehalulose and sucrose. The test consists of oxidizing sugars by potassium ferricyanide ion in alkaline solution. Sugar solutions are reacted with standardized ferricyanide solution and titrated with ceric sulphate with ferrion as an indicator. The tests of total reducing sugars or total sugar content give no indication of the type of sugars involved in the stickiness phenomenon. In addition, melezitose being a non-reducing sugar is not detected by this method which leads to false positive results. Furthermore, this test gives no indication of the distribution of the sugars on the fiber. Since stickiness is mainly due to localized high sugar concentration (insect excrement) it is extremely important to get distribution information.
Another testing procedure is the High Performance Liquid Chromatography (HPLC), which is performed by first extracting sugars with water. By using an appropriate eluant, the sugar solution goes through a column where a separation takes place on the basis of molecular weight and steric arrangement. HPLC profiles indicate the amounts of individual sugars on the lint. Having a similar disadvantage as the Perkins test, this test cannot give information about sticky deposit distribution and therefore is not a good predictor of stickiness in the mill. In addition, this time consuming test is costly, which limits its utilization to research laboratories.
The Minicard test (Perkins, 1990) was approved by The International Textile Manufacturers as a reference test in 1990. A sample of 10 grams is processed through the minicard at 55% relative humidity. The sample is rated for stickiness depending upon its behavior as the card web passes between the stainless steel delivery rolls. For accurate evaluation, the instrument should be subjected to frequent cleaning. Consequently, this highly operator sensitive technique is not adequate for large scale testing.
The Fiber Contamination Tester (FCT) is derived from the minicard principle. A 3 grams sample (hand-sliver shaped) is processed through a micro-card at 65% relative humidity. Then the cotton web passes between 2 crush-rolls. The friction of the brushes (cleaning device) increases the temperature of the crush rolls and allows the honeydew to stick to the crush rolls. This unintentional temperature change makes the instrument a kind of xe2x80x9cThermodetectorxe2x80x9d. The sticky deposits on the rolls are detected using laser beams. A cleaning device of brushes and knives removes the sticky deposits. Software analyses the electronic signal, providing the user with the number of deposits along with their size. The FCT is designed such that the instrument is very quickly contaminated with honeydew rendering the results questionable.
The Sticky Cotton Thermodetector (SCT) was approved as a reference test by the International Textile Manufacturers Federation in 1994. This thermo-mechanical method combines the effect of heat and pressure applied to a sample of cotton placed between two aluminum foils. When the temperature increases, the cotton releases its water, which is absorbed by the sticky spots making them stick to the foils. However, this instrument is operator sensitive and slow.
The High Speed Stickiness Detector (H2SD) is based on the SCT principle. First, a sample of cotton weighing between 3.0 and 3.5 g is opened using a rotor type opener. The mass of opened fiber is then shaped into a rectangular, even pad of fibers. This pad is deposited by the system on aluminum foil. Then, the sample passes successively in front of 4 stations. A hot pressure is applied to the sample (54 degrees C, 30 seconds). The combination of the free water molecules in the cotton lint and the temperature differential between the heat applied and the aluminun foil produces a thin layer of humidity on the sheet of aluminum. The sticky points in contact with the aluminum are fixed in place by pressure exerted at ambient temperature. The cotton is then removed and the sticky spots are counted and sized by an image analyzer. This testing procedure is undesirable because it may give false positive test results. This process does not give a realistic interpretation of the stickiness of the cotton at machine operating temperatures. Certain cottons contain sugar deposits that cause sticky spots at elevated temperatures, such as 54xc2x0 C., but do not have sticky deposits at lower, operating temperatures, such as 27 xc2x0 C. This false result forces cotton growers to sell their crop to spinners at a discount.
The present invention overcomes the above-mentioned problems by developing a method that is based on the detection of cotton stickiness at multiple temperatures. By testing the cotton stickiness at two or more temperatures, different grades of cotton can accurately be distinguished to allow growers and spinners to manage their crops.
Cotton may be tested for sticky deposits of sugars using at least two different temperatures. The cotton is tested at a lower temperature, preferably 27 xc2x0 C. or 34 xc2x0 C., to determine the amount of trehalulose-rich honeydew droplets. The cotton is then tested at a second temperature, preferably 54 xc2x0 C., to determine the amount of non trehalulose-rich honeydew droplets and physiological sugar. The amount of sticky spots at the two temperatures are compared to yield an accurate grading of cotton.
Due to the different thermal properties of sugars, the lowest temperature will render trehalulose (mainly present in white flies honeydew) stickier than the other types of sugars. Alternately, the higher temperatures will render the other sugars, present on the contaminated lint, stickier. The honeydew droplets having a high percentage of trehalulose will stick at any temperature. The lower the trehalulose percentage is in those droplets, the lower is the xe2x80x9csticky potentialxe2x80x9d at low temperature. The differential between two or more readings at different temperatures will show the type of contamination and will allow the spinners to better predict the processing troubles to be expected in the mill and to use this information for bale management.